1. Field of the Invention
The present invention generally relates to terminating resistance adjusting methods, semiconductor integrated circuits and semiconductor devices, and more particularly to a terminating resistance adjusting method for adjusting a terminating resistor provided within a semiconductor integrated circuit, a semiconductor integrated circuit that employs such a terminating resistance adjusting method, and a semiconductor device having such a semiconductor integrated circuit.
2. Description of the Related Art
FIG. 1 is a diagram for explaining an example of a conventional data transmission system. In FIG. 1, each transmitting and receiving system 1 is provided with a semiconductor device (or a semiconductor chip) 2 having a semiconductor integrated circuit, a terminating resistor 3 and an external terminal 4. The two transmitting and receiving system 1 are connected via a transmission line 5 that connects to the external terminals 4 thereof.
The terminating resistor 3 is provided for impedance matching, as a noise countermeasure, when making a high-speed data transmission in such a data transmission system. Generally, the terminating resistor 3 that is necessary for making the high-speed data transmission via the transmission line 5 is required to have a highly accurate resistance.
However, according to the structure in which the terminating resistor 3 is externally connected to the semiconductor device 2, there was a problem in that the cost of the transmitting and receiving system 1 becomes high. Hence, a Japanese Laid-Open Patent Application No. 2003-143002 proposes a method of providing the terminating resistor within the semiconductor device.
According to the method proposed in the Japanese Laid-Open Patent Application No. 2003-143002, the terminating resistor is used to generate a certain potential when calibrating the terminating resistor within the semiconductor device, and it is necessary to supply a current directly to the transmission line. But since a pull-down resistor is connected in parallel to the transmission line, it is only possible to obtain a calibration result including the pull-down resistor when the calibration is made by supplying the currently directly to the transmission line. Consequently, there was a problem in that an accurate calibration cannot be made.